Soft Plasmons with Stretchable Spectroscopic Response Based on Thermally Patterned Gold

Supporting information

Soft plasmons with stretchable spectroscopic response based on thermally patterned gold nanoparticles

Xinping Zhang*, Jian Zhang, Hongmei Liu, Xueqiong Su, and Li Wang

Institute of Information Photonics Technology and College of Applied Sciences, Beijing University of Technology, Beijing 100124, P. R. China

*Email:

Figures S1 (a) and (b) shows the scanning electron microscope images of the grating structures fabrication using solution-processed methodfor an annealing temperature below 200 oC and above 350oC, respectively. At a lower annealing temperature than 200 oC, although the ligands have been sublimated completely, the gold nanoparticles get molten to aggregate into larger ones that cannot become molten anymore. Thus, the strong confinement mechanisms based on molten gold cannot take effect at such a low annealing temperature. As results, gold nanoparticles are distributed around the grating grooves without forming homogeneous gold nanolines, as shown in Fig. S1(a). However, when the annealing temperature is increased further to above 350 oC, the gold nanoparticles are melted completely, and the molten gold is pulled into the grooves by the strong surface tension, as shown in Fig. S1(b).

Fig. S1 SEM images of the MPC structures annealed at a temperature lower than 200 oC (a) and above 350 oC (b).

Figure S2 (a) and (b) shows the optical extinction spectroscopic measurements on the transferred MPCs on PDMS substrates before the coating of the PMMA waveguide layer for TM and TE polarizations, respectively. Thus, Fig. S2 shows the angle-resolved tuning performance of the optical extinction spectra of MPCs on a bare PDMS substrate, where the incident angle is increased from 0 to 30 degrees. Plasmon resonance without Fano coupling is observed for TM polarization in Fig. S2(a), which is centered around 666 nm. No obvious plasmon resonance is observed for TE polarization, as shown in Fig. S2(b).

Fig. S2Optical extinction spectra at different incident angles (0~30o)measured on the MPCs directly transferred to the PDMS substrates before deposition of the PMMA waveguide layer for (a) TM and (b) TE polarization. The transmission spectrum through a bare PDMS plate is used as the blank in the optical extinction calculation.

Figure S3 shows results of the stretching experiment by optical extinction spectra of MPCs on PDMS substrates at an incident angle of (a) i=0 and (b) i=6o, where the stretching amount of PDMS substrate were increased from =0 to =1000 mm. The Fano resonance, which results from the coupling between the waveguide resonance and plasmon resonance modes and is recognized by a narrow-band dip in the optical extinction spectrum, shifts to the red with increasing the stretching amount. This red-shift process is indicated and guided by the red arrows in Fig. S3(a) and (b). In the measurement results in Fig. S3, the transmission spectrum through a bare PDMS plate is used as the blank in the optical extinction calculation.

Fig. S3Optical extinction spectra at (a) i=0 and (b) i=6ofor different stretching amounts (=0~1000 m). The transmission spectrum through a bare PDMS plate is used as the blank in the optical extinction calculation.